Hello Abdul ,
It means that USB camera is not opened in default demo image.
you can do it like below, and re-compile android images via android source code and bsp.
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Set it in init.rc like below:
setprop back_camera_name uvc
or
setprop front_camera_name uvc
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then program you android images into eMMC / SD card.
Hope above innformation is helpful for you.
Have a nice day!
B.R,
weidong